A sample of 121 mother-infant pairs were studied in order to identify the primary dimensions of mother-infant interaction and to relate these data to other information obtained in a longitudinal program on family development. Data consists of interviews and questionnaires with expectant mothers during the third trimester of pregnancy; time-sampled codings from two 6-hour home observations when the infants were three months of age; postpartum interviews and questionnaires administered to the mothers; a series of laboratory procedures conducted in the homes to assess stranger and separation reactions, imitation, socialization, and exploratory behavior when the infants were about eleven months of age. Relations were found between maternal attitudes and maternal behavior and these variables interacted with the socioeconomic status of the mother and with the sex of the infant. Results have also been obtained demonstrating a positive correlation between the frequency of contingent maternal behavior toward infant vocalizations in the home and the rate at which these infants vocalize to similar contingent reinforcements in a laboratory procedure. BIBLIOGRAPHIC REFERENCE: Moss, H.A.; Infancy: Personality Development. In Wolman, B. B. (Ed.): International Encyclopedia of Neurology, Psychiatry, Psychoanalysis, and Psychology. New York, Van Nostrand Rainhold, 1977, Vol. 6, pp. 42-46.